1. Technical Field
The present invention relates to a common mode filter, and more particularly, to a common mode filter having an ESD protection capability.
2. Description of the Related Art
As technologies evolve, electronic devices such as a mobile phone, a home appliance, a personal computer (PC), a personal digital assistant (PDA), a liquid crystal display (LCD), and the like, are being changed from an analog manner into a digital manner, and data processing speed is being increased as the amount of processing data increases. Accordingly, high-speed signal transmission interfaces such as a USB 2.0 interface, a USB 3.0 interface, and a high-definition multimedia interface (HDMI) are widely employed. Such interfaces are currently used in many digital devices such as personal computers and digital high quality televisions.
Unlike single-end transmission systems which have been used for ages, theses high-speed interfaces employ a differential signal system which uses a pair of signal lines to transmit differential signals (differential mode signals). However, digitalized, high-speed electronic devices are sensitive to the environments so that signal distortion due to high-frequency noise often occurs.
In order to remove such noise, filters are installed in electronic devices, and especially common mode filters are being widely used to remove common mode noise in high-speed differential signal lines. The common mode noise refers to the noise occurring in differential signal lines, and the common mode filters remove the common mode noise which was not removed by existing filters.
Recently, since high-speed, digital interfaces process minute signals at high transmission rate, very sensitive IC should be used for electro static discharge (ESD) generated when different devices are connected to and separated from each other.
In this regard, Patent Document (Korean Patent Laid-Open Publication No. 10-2010-0037000) proposes a common mode filter having an ESD protection layer. As shown in FIG. 3 of the Patent Document, the ESD protection layer 12b is further provided under the common mode filter layers 12a, and the ESD protection layer includes the ESD absorption layer 30 to function as an ESD protection material. With this configuration, an overvoltage signal due to static electricity exits through gap electrodes 28 and 29 which maintains a predetermined gap with lead conductors, and thereby protecting spiral conductors 17 and 18 in the common mode filter layer.
In the common mode filter disclosed in the Patent Document, however, it is difficult to implement a thinned chip since the separate ESD protection layer for ESD protection is provided in the common mode filter. Moreover, the lead conductor maintaining a predetermined gap with the gap electrodes 28 and 29 is connected to one terminal, i.e., an input terminal of the pair of external terminals (e.g., 13a and 13b) with respect to e.g., one spiral conductor 17, ESD protection is not possible when an overvoltage signal is applied to the other terminal of the external terminals, i.e., an output terminal.